1. Field of the Invention
The present invention relates to a light emitting element driving circuit.
2. Description of the Related Art
Lighting equipment using an LED (Light Emitting Diode) may use an LED driving circuit which drives an LED while improving the power factor (See Patent Document 1, for example).
FIG. 11 is a diagram illustrating a common configuration of an LED driving circuit. When an AC voltage Vac of a commercial power supply is supplied to a full-wave rectifying circuit 300, the full-wave rectifying circuit 300 applies full-wave rectification to the AC voltage Vac for output. Resistors 310 and 320 divide the rectified voltage Vrec subjected to the full-wave rectification at the full-wave rectifying circuit 300 and outputs the result as a reference voltage Vref. The switching circuit 330 turns on the NMOS transistor 340 at predetermined intervals, and the switching circuit 330 turns off the NMOS transistor 340 when a voltage Vs according to the current flowing through an LED 350 becomes the reference voltage Vref. Since the reference voltage Vref and the rectified voltage Vrec are similar in an LED driving circuit 200, the waveform of the current flowing through the LED 350 also becomes similar to the waveform of the rectified voltage Vrec. Therefore, the LED driving circuit 200 can drive the LED 350 while improving the power factor.
The amplitude of the AC voltage Vac of the commercial power supply may greatly vary within a range of, for example, 90 to 140V. In such a case, the level of the reference voltage Vref also varies greatly resulting with cases where the current flowing through the LED 350 vary significantly, and the brightness of the LED 350 largely deviates from the desired brightness.